If someone who had been an infantryman wanted to take a couple of gun buddies out and show them how to assault a bunker using a big cardboard box a baseball and their favorite long guns it wouldn't be a crime unless they were planning on assaulting the post office or something. If, as is much more likely, the guy was just showing off or trying to give them a feel for how the Army or Marine Corps trains, it wouldn't be a problem.

Unless one of them had a heart attack while doing three to five second rushes.